Sensitive photoelectric control for signal devices



Oct. 12, 1948. v T. K. RIGGEN 2,450,990

7 SENSITIVE PHOTOELECTRIC CONTROL FOR SIGNAL DEVICES Filed June 4, 1947 l N uvmvroge.

J 07% BY.

T ORNE Y Patented Oct. 12, 1948 snnsr'rrvn rnoronnacrmc con'raor. roa

. srcmr. DEVICES Theodore x. Riggen, Elmira, N. r. Application June 4, 1947, Serial No. 752,511

The present invention relates to a sensitive photo-electric control and more particularly to photo-electric means for actuating a signal when the intensity of illumination of the device falls below a pre-determined critical value.

Various forms of photo-electric devices for signailing changes in illumination have been heretofore produced, and found useful in detecting departures from uniformity in color of objects, andvariations in translucence of liquids and gases, etc; While such. devices as heretofore constructed have considerably greater 'discrimina tion than the human perceptions, there has existed a demand for instruments of greater sensitivity and uniformity of response than has been found possible with the conventional types of photoelectric circuits.

.ode 2|. The. screen grid 25 of the tube I5Iis maintained at a suitable positive potential by connection to the power supply E through resis- It is an object of thepresent invention to pro;

vide anovel photo-electric control of a signalling device which is extremely sensitive to small changes in illumination, while being simple in construction, stable in operation and readily adjustable inrespect to the critical light value.

It'is another object to provide such a device in which a photo-electric cell is used to control the bias on the grid'of a sharp cut-off amplifier tube, and a signal amplified by said tube is used to control the operation of a signalling device.

It is another object to provide such a device which is-readily adjustable so as to operatethe amplifier tube close to its point of cut-oif at all times, and thereby takes full advantage of the sensitivity of the tube to slight changes in grid bias while in that condition. f

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawing in which the figure illustrates diagrammatically a preferred form of the present invention. I In the drawing there is illustrated a signal circuit indicated generally by numeral I, comprising alphoto-electric cell or tube 2,a resistor 3 connected to the cathode of the tube, a second resistor 4 connected to the anode of the tube and a source of alternating voltage 5 connected by the leads 6 and 'l to the resistors 3' and 4 respectively. As here shown the source of alternating voltage is in the form of the secondary of a transformer 8, the primary 9 of which is connected to any i' convenient source of alternating current such as the 110 volt power mains II and 'I2.

4 Claims. (01. 171-311) the conductivity ofwhich varies in accordance with the intensity of illumination.-

The anode of the photo cell is connected through a condenser l3 to the control grid ll of an amplifier tube l5. vTube .I5 is preferably of the pentode type, and the plate l5 thereof is .con-

nected by means of a. lead I! and resistors l8 and L9 to a suitable source of plate voltage indicated at E.

The cathode of tube I5 is connected to the ground through a resistor 22 bridged by. ai'condenser 23, and the grid 14 of the tube is also grounded through a resistor 24, resistors 22and 24 being of such value as to maintain the grid I4 at a suitable negative bias with respect to the oathnected to the grid 32 of a second amplifying tube 33 thus forming a resistance couplingfrom tube.

I5 to tube 33 the gain of which is adjustable by the potentiometer 29.

Cathode 34 of tube 33 is connected to the ground through resistor 35 and condenser 36,'and the plate 31 is connected by a lead 38 to' a resistor 39 which is connectedinturn by a lead 4| to the voltage supply E. The plate lead 38 is connected through a coupling condenser 42 to one cathode 43 of a twin rectifier tube 44 such as the type commonly designated 6H6. The corresponding anode 4|l of tube 44 is connected to the ground by a lead 45. The coupling condenser. 42'is also connected by a lead 46 to a voltage divider formed by resistors. 41 and 48, the resistor 48 being grounded, and.

resistor 41 being connected by a lead-43 to the control grid 5| of a sharp cut-ofi amplifier tube.

52 such as that known commercially as type 6SJ7. The control grid 5| is also connected through a condenser 53 to a signal generator S 7 whereby a constant alternating voltage signal is The photo cell 2 is arranged in any conven ticinal manner to be illuminated by the light, the

intensity of which is to be measured, "and it will impressed on said grid. The cathode 54 of tube 52 is maintained at a suitable positive voltage with respect to ground by means of a connection 55 to a voltage divider formed by resistors 56 and 51, resistor 58 being connected to the plate voltage supply E,- and resistor 51 being grounded.

'I'hefscreen'grid' 55.01 tube 52 is connected to the plate-voltage supply through resistors 59 and 5!, and is connected tothe ground through-a con-' id being connected to denser 62. The plate 68 of tube 62 is connected by a lead 64 to a resistor 65 which is also connected to the resistor 6i so as to connect the plate to the power supply E.

The plate lead 84 is connected by a coupling condenser 65 to the grid 61 of an amplifying tube 68, the cathode 69 of which is grounded, and the plate ll of which is connected to the power supply E through the primary 12 to a transformer 13. One terminal of the secondary 14 of transformer I3 is connected to the ground as indicated at 15 and the opposite terminal is connected by a lead 16 to the second cathode ll of the twin rectifier tube 44.

The corresponding plate 18 of rectifier 44 is connected by a lead 19 to the control grid 8| of a gaseous discharge tube or thyratron 83 such as the type known as 884. The thyratron 83 is used to actuate a signalling device or alarm here shown in the form of an electric bell 84, and for this purpose the cathode 85 of said tube is connected by the lead 86 to one terminal of the bell 84, the opposite terminal of which is grounded through a lead 81. The plate 88 of tube 83 is connected by a lead 89 to a resistor 91, and the resistor is connected by a lead 92 to the positive terminal of a sou ce of voltage V, the negative terminal of whicl. is grounded as indicated by 93. A storage condenser 94 is connected between the plate 88 of tube 83 and the ground whereby the condenser is charged by current traversing the resistor Si when the tube 83 is non-conductive, and said condenser discharges through the tube 83 when it becomes conductive, thereby actuating the signalling device 84. In order to provide a visual signal as well as an audible signal, the plate lead 89 of tube 83 is connected through a condenser 95 to the inner grid 96 of a strobotron tube 91 such as that known as type 93lPl, said grid being connected to ground through a resistor I00. The cathode. 98 of the strobotron is grounded as indicated at 99. Its outer grid IDI is connected to the power source V through a resistor I02 and lead I03, and

its plate 164 is connected to the resistor I02 through a second resistor )5. The plate I04 is also connected to the ground through a condenser I06 whereby the strobotron will fire and produce a visible signal when the thyratron 83 discharges.

In the operation of the device the photo-electric cell 2 is located in position to be illuminated by the source of light to be measured, andis activated by an alternating voltage supply through the transformer 8. Assuming that light of a given intensity strikes thephoto cell 2,'a corresponding number of electrons will be released from the cathode of said tube, and current will accordingly. pass from the transformer 8 through resistor 4, photo cell 2 and. resistor 3 back to the transformer on that half of the oscillation wherein the anode of the photocell is positivewith respect to the cathode. This will develop a til and cathode 2| of tube ll as an alternating current signal with one end fiat. This signal will then be amplified by the tube It and by means of the coupling condenser 28 will be expressed across the potentiometer 23. That portion of this signal existing between the arm 3! of the potentiometer and the ground will be expressed between the grid 32 of tube 33 and its cathode 34 whereby it will beamplified by the tube 33 and by means of the coupling condenser 42 will be expressed across the resistor 48. The signal across resistor '48 would therefore be an alternating current signal except for the rectifying action of the tube 44. During that half of the signal expressed across resistor 48 wherein the cathode 43 of rectifier 44 is negative with respect to its plate 40, current will flow through the rectifier rather than through resistor 48 since in this direction the rectifier has a low impedance compared to said resistor. During the other half of the signal no current will flow through the rectifier 44 and hence the current will be forced to flow through resistor 48. Condenser 42 and resistor 48 therefore act as a filter for the pulsating current across resistor 48 so as to maintain a substantially constant direct current through said resistor so long as the illumination of the photo cell 2 remains constant.

The ungrounded end of resistor 48 is the positive end, and the voltage drop through the resistor is thus used by virtue of the connection through the resistor 41 to bias the grid 5| of amplifier tube 52 positive with respect to ground. The voltage dividers '56 and 51 maintain the cathods 54 of tube 52 positive with respect to ground, so that the amplification factor of tube .resistor 4 will decrease, decreasing the signal across resistor 24 and thereby decreasing the positive bias ofthe grid-5i of amplifier tube 52. This causes saidgrid to appear more negative with respect to t e cathode 54 of said tube and the gain of the ube will be reduced. The output of'the second amplifier tube 88 will therefore voltage across the resistor 4. During the other I half of the oscillation wherein the anode of the photo cell is negative with respect to the cathode, there will be no current flow, and hence no volt-.

age across the resistor4. A signal will then have been developed across resistor 4 which will have the character of half of a sine wave. This signal also appears across the resistor 24, by virtue of. the coupling condenser resistor 24 and therefore between the grid l4 l3, which condenser moves the zero line of the signal from its normal position to a position half-way between the extremes. so that the signal;appears across the be reduced. Reduction of the out-.put of this tube,reduces the out-put of transformer 13 which reduces the rectified signal through the cathode and anode I1. I8- of tube 44 which is expressed across resistor 80 and. condenser 90. This rectified; out-put may be assumed, at the initial light intensity, to have held the grid 8| of the thyratron 83 at a substantially negative bias with respect to the. cathode 85 which prevents the tube from becoming conductive. The lowered intensity of the light striking the photo cell 2 causes a reduction in" this negative bias on the grid 8i, and when said reduction is sufficient the tube will discharge.

Condenser '94. is

- power source V through the resistor 9|. When the thyratron 83bec'omes conductive, condenser 94 discharges through the .tube andthejslgnal device 84, thus operating thelatter. The amount 4 of'current permitted to pass by the resistor 8| is insufilcient to maintain the tube 83 conductive,

thereforefassoon as condenser 34 is discharged the tube will heal and become non-conductive normally charged from the whereupon the condenser 94 will be recharged through resistor 8| until the critical voltage is reached whereupon it will again discharge through the tube 83, such discharges continuing as long as the bias of the grid 8| of tube 83 is sufficiently small with respect to the cathode 85 to permit the tube to fire.

With each discharge of condenser 94, through the signalling device 84 and tube 83, the resistance through the tube 83 will approach zero and the current through resistor ill will increase. The voltage drop across resistor 9| will therefore be increased and this voltage, through condenser 95 will be expressed across resistor I and-on the grid 96 of tube 91. This voltage will initiate break-down in the tube and cause it to fire.

If the light intensity at the photo cell continues to decrease or remains at that level, the signalling device will continue to operate. When the light intensity increases above the critical point, the bias on the grid 8| will again block the thyratron 83 and the signalling device will cease to operate,

Although but one form of the invention has been shown and described in detail it will be understood that other embodiments are possible and that various changes may be made in the design and arrangement of the parts without departing from the scope of the invention.

What is claimed is:

1. In a photo-metric device a signal generating circuit including a source of alternating current, a resistor and a photo-sensitive electronic tube, means for amplifying and rectifying the signal produced by said circuit so as to produce a positive voltage which varies in accordance with the intensity of illumination of said photo-sensitive tube; a second amplifying and rectifying means including an amplifying tube having a cathode, an anode and a control grid; means for impressing a substantially constant alternating signal voltage on said grid, means for biasing'the grid negatively I with respect to the cathode to render the tube non-conductive, means for filtering the amplified and rectified signal from the signal circuit and impressing it on said grid of the amplifying tube so as to render the amplifying tube conductive when the photo-sensitive tube receives light of a pre-determined intensity, a signalling device, and means responsive to a reduction in out-put of the second amplifying means for causing actuation of said signalling device.

2. A photo-metric device as set forth in claim 1 I including means for adjusting the gain of the first mentioned signal amplifying means so as to cause a pre-determined illumination of the photo-sensitive tube to render said amplifying tube conductive.

3. A photo-metric device as set forth in claim 1 in which the signalling device includes a thyratron, an alarm device actuated by the discharge REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date -,-2,084,186 Braden June 15, 1937 2,122,850 Thompson July 5, 1938 2,234,011 Shepard Mar. 4, 1941 2,284,289 Lindsay May 26, 1942 2,372,062 Dorsman Mar. 20, 1945 2,391,532 Wilmette Dec, 25, 1945 2,415,175 Hurley Feb. 4, 1947 

